The present disclosure relates to an optical fiber preform and a method of manufacturing an optical fiber.
An optical fiber is manufactured by heating and melting one end of an optical fiber preform made of glass in a fiber drawing and heating furnace, drawing the glass optical fiber from the one end, and forming a coating made of resin or the like on an outer circumference of the drawn glass optical fiber by using a die.
However, a tip portion of the optical fiber preform may include a defective portion where a ratio between an outer diameter of a core portion and an outer diameter of a cladding portion deviates from a standard. A glass optical fiber drawn from such a tip portion may not be used as a product because the core diameter and the cladding diameter deviate from the standard. Such a tip portion of the optical fiber preform is used to draw a fiber to adjust various conditions of fiber drawing when a manufacturing process of the optical fiber is started.
When the manufacturing process of the optical fiber is started, a drawing speed of the glass optical fiber (a fiber speed) is set to a low fiber speed at first because of a reason such as to adjust various conditions of fiber drawing. Thereafter, when conditions to draw a non-defective glass optical fiber are satisfied, the fiber speed is accelerated to a predetermined high fiber speed. Thereafter, the fiber speed is controlled to be constant at the predetermined fiber speed and a glass optical fiber that is made into a product is manufactured.
Here, a technique is disclosed in which a shape of the tip portion of the optical fiber preform is formed to be able to shorten a time of fiber drawing of the tip portion in order to shorten a start-up time of the manufacturing process of the optical fiber and draw a non-defective glass optical fiber in an early stage (for example, see JP 2002-80238 A). Further, JP 2003-327440 A discloses a technique in which a shape of a tip of a glass tube that forms an outer circumference of the optical fiber preform is previously made close to a meniscus shape that is a shape of the optical fiber preform melted during fiber drawing.
By the way, to improve efficiency of the manufacturing process of the optical fiber, it is required to further shorten the start-up time of the manufacturing process of the optical fiber. In particular, in a case of an optical fiber preform whose diameter is enlarged to manufacture the optical fiber at low cost, the volume of the tip portion of the optical fiber preform is also large. As a result, the start-up time of the manufacturing process of the optical fiber until a non-defective glass optical fiber is drawn becomes long. Such elongation of start-up time causes excessive consumption of raw material because a lot of optical fiber that does not become a product is drawn, so that it is further required to shorten the start-up time.
There is a need for an optical fiber preform that may shorten the start-up time of the manufacturing process of the optical fiber and a method of manufacturing the optical fiber by using the optical fiber preform.